The invention relates to a method of injecting fuel into the combustion chambers of an internal-combustion engine particularly a diesel engine, by means of a fuel injection system which contains a number of fuel injectors each comprising an injection valve and a common feed and storage line which supplies the individual fuel injectors by way of respective high-pressure lines with highly pressurized fuel and itself is acted upon by highly pressurized fuel by way of a high-pressure pump, the feeding of the fuel taking place from the storage line by way of one or more high-pressure reservoirs, and the beginning and end of the injection of the fuel into the combustion chambers being controlled by opening and closing the injection valves of the fuel injectors. The invention also relates to a fuel injection system for an internal-combustion engine according to particularly a diesel engine, which contains a number of fuel injectors each comprising an injection valve and a common feed and storage line which supplies the individual fuel injectors with highly pressurized fuel and itself is acted upon by highly pressurized fuel by way of a high-pressure pump, as well as one or more, particularly two high-pressure reservoirs which are, in each case, provided in the high-pressure lines leading to the fuel injectors and have a defined fuel storage volume, the beginning and end of the injection of the fuel into the combustion chambers being controlled by opening and closing the injection valves of the fuel injectors.
In the case of internal-combustion engines, particularly in the case of diesel engines, a type of fuel injection has increasingly been used in which a common feed and storage line (common rail) is acted upon by highly pressurized fuel by means of a high-pressure pump, and the highly pressurized fuel is fed by the latter by way of respective high-pressure lines to a number of fuel injectors which each comprise an injection valve. The beginning and the end of the injection of the fuel into the combustion chambers of the internal-combustion engine are controlled by the opening and closing of the injection valves provided in the fuel injectors. In addition, high-pressure reservoirs having a defined fuel storage volume may in each case be provided in the high-pressure lines leading to the fuel injectors. This type of a fuel injection is known, for example, from German Patent Document DE 197 12 135 C1.
The increasingly strict demands with respect to a limitation of pollutant emissions of internal-combustion engines have the tendency to require higher and higher injection pressures. The pressure which is maximally permissible in view of the stress on the material in a fuel injection system of the above-mentioned type is determined by the peak pressures occurring in the system. The highest pressure peaks occur in the fuel injector at the end of the injection. The cause is the so-called ram or surge pressure, which occurs during the closing of the injection valve and may be up to 400 bar above the system pressure. This means that conventionally the system pressure of the fuel injection system has had to be planned to be by up to the above-mentioned 400 bar lower than the peak pressure maximally acceptable with respect to the stress to the material.
The object of the invention is an improved method of injecting fuel into the combustion chambers of an internal-combustion engine as well as an improved fuel injection system for an internal-combustion engine.
The object is achieved by means of a fuel injection method limiting continued flow of the fuel during injection such that a defined lowering of fuel pressure existing in a fuel injector takes place from an initial pressure p1, which is slightly lower than a system pressure, to a second pressure p2 at a second point in time T2 when closing of a fuel injector valve starts, so that such pressure which rises because of ram pressure during the closing of the injection valve at the end of the injection in the fuel injector does not exceed a defined value. This object is also achieved by means of a fuel injection system wherein the fuel storage volume of the high-pressure reservoirs and the flow resistance of the high-pressure lines lead from the common feed and storage line to the high-pressure reservoirs, while taking into account the maximal injection quantity and duration, are dimensioned such, during the injection, a lowering of the fuel pressure existing in the fuel injector takes place from an initial pressure p1, which is slightly lower than the system pressure, to a fuel pressure p2 at a second point in time when the closing of the injection valve starts, so that the pressure, which rises as a result of the ram pressure during the closing of the injection valve at the end of the injection in the fuel injector, does not exceed a defined value.
The invention provides a method of injecting fuel into the combustion chambers of an internal-combustion engine, particularly a diesel engine, by means of a fuel injection system which contains a number of fuel injectors each comprising an injection valve and a common feed and storage line which supplies the individual fuel injectors by way of respective high-pressure lines with highly pressurized fuel and itself is acted upon by highly pressurized fuel by way of a high-pressure pump, the beginning and end of the injection of the fuel into the combustion chambers being controlled by opening and closing the injection valves of the fuel injectors. According to the invention, it is provided that, during the injection, a defined lowering of the fuel pressure existing in the fuel injector takes place, so that the pressure, which rises because of the ram pressure during the closing of the injection valve at the end of the injection in the fuel injector, does not exceed a defined value.
The defined lowering of the fuel pressure in the fuel injector preferably takes place to such a value that the pressure, which rises because of the ram pressure during the closing of the injection valve at the end of the injection in the fuel injector, does not exceed the fuel pressure, particularly the system pressure P0, existing in the fuel injector at the beginning of the injection.
According to an embodiment of the method according to the invention, it is provided that the feeding of the fuel from the common feed and storage line to the fuel injectors takes place by one or more, particularly two high-pressure reservoirs provided in the high-pressure lines leading to the fuel injectors and having a defined fuel storage volume, and that the defined lowering of the fuel pressure existing in the fuel injector takes place by limiting the continued flow of the fuel in the high-pressure lines leading from the common feed and storage lines to the high-pressure reservoirs.
When two high-pressure reservoirs are used, the high-pressure reservoir situated closer to the injector is preferably constructed with a smaller volume than the high-pressure reservoir situated farther upstream. A quantity-limiting valve, which is preferably situated downstream of the respective high-pressure reservoir, is assigned to at least one high-pressure reservoir.
According to an embodiment of the method according to the invention, the limiting of the continued flow of the fuel takes place by throttling points provided in the high-pressure lines leading from the common feed and storage line to the higher-pressure reservoirs.
According to another embodiment, the limiting of the continued flow of the fuel takes place by dimensioning the diameter D2 of the high-pressure lines leading from the common feed and storage line to the high-pressure reservoirs.
It is an advantage of the injection method according to the invention that a high injection pressure can be used at the beginning of the injection without causing an unacceptable overstressing of the material in the fuel injector.
Furthermore, by means of the invention, a fuel injection system for an internal-combustion engine, particularly a diesel engine, is created which contains a number of fuel injectors each comprising an injection valve and a common feed and storage line which supplies the individual fuel injectors by way of respective high-pressure lines with highly pressurized fuel and itself is acted upon by highly pressurized fuel by way of a high-pressure pump, as well as, in each case, one or more, particularly two high-pressure reservoirs which are provided in the high-pressure lines leading to the fuel injectors and have a defined fuel storage volume, the beginning and end of the injection of the fuel into the combustion chambers being controlled by opening and closing the injection valves of the fuel injectors. According to the invention, it is provided that the fuel storage volume of the high-pressure reservoirs and the flow resistance of the high-pressure lines leading from the common feed and storage line to the individual high-pressure reservoirs, while taking into account the maximal injection quantity and duration, are dimensioned such that the pressure, which rises as a result of the ram pressure during the closing of the injection valve at the end of the injection in the fuel injector, does not exceed a defined value.
The fuel storage volume of the high-pressure reservoirs and the flow resistance of the high-pressure lines leading to the high-pressure reservoirs are preferably dimensioned such that the pressure rising as a result of the ram pressure during the closing of the injection valve at the end of the injection in the fuel injector does not exceed the fuel pressure, particularly the system pressure P0, existing at the beginning of the injection in the fuel injector.
According to an embodiment of the fuel injection system according to the invention, it is provided that the flow resistance of the high-pressure lines leading from the common feed and storage line to the high-pressure reservoirs is determined by throttling points.
According to another embodiment of the invention, it is provided that the flow resistance of the high-pressure lines leading from the common feed and storage line to the high-pressure reservoirs is determined by their diameter D2.
As in the case of the fuel injection method according to the invention, it is also an important advantage of the fuel injection system according to the invention that high pressures can be used at the beginning of the injection without causing an unacceptable overstressing of material in the fuel injectors.
For a fuel injection without the lowering of the fuel pressure existing in the fuel injector toward the end of the injection according to the invention, if equally high initial pressures are to be achieved, the fuel injectors would have to be designed for the significantly higher pressures which arise because of the ram or surge pressures occurring during the closing of the injection valve.
In the following, an embodiment of the invention will be explained by means of the drawing.